1. Field of the Invention
This invention relates to optical communication networks and more in particular to an optical communication network which comprises a plurality of nodes and optical transmission lines for interconnecting the plurality of nodes thereby allowing to transmit an optical signal from a source node to a destination node or nodes.
2. Description of the Prior Art
Two different types of communication network system are well known in the art; they are a loop network system and a coaxial bus network system. Typically, the loop network system is described in "A Ring Network" by D. J. Farber, Datamation, Vol. 21, No. 2, Feb. 1975, 44-46 and the coaxial bus system is described in "Ethernet: Distributed packet switching for local networks" by R. M. Metcalfe and David R. Boggs, CACM, Vol. 19, No. 7, July 1976, 395-404.
For high speed applications of these network systems, an attempt has been and is being made to use optical fibers as interconnections between the nodes, but none has yet been successful from various reasons. For example, it is true that the loop network system has a capability of high speed transmission and a noise-resistant characteristic; however, since all of the nodes are connected in series by interconnecting transmission lines, there is a grave problem in reliability. That is, if a node or an interconnecting line fails, the whole system becomes inoperative. Moreover, once the network is completed, a further network expansion is difficult to make.
On the other hand, the bus coaxial network system is adaptive for expansion and is highly reliable, but it suffers from disadvantages such as difficulty in implementing high speed transmission and high susceptibility to noises. It is well recognized that an application of optical fibers to the Ethernet system is hindered mainly by technological difficulty because of the absence of a high impedance optical fiber "T" connector.